Arctic Alaska’s Conservation Conundrum

By  Dr. Joel Berger

The Arctic wind blows hard on the snow-covered plains a few hundred miles southwest of Prudhoe Bay.  It’s eight degrees in the winter chill. Despite global warming, I am still quite cold.  I watch the tracks of the grizzly bear disappear upslope as they narrow toward a newborn calf. Out of my field of vision its mother, a muskoxen – the quintessential land animal of the Arctic – stands guard. But it is no match for the powerful predator looking for its next kill.

Grizzly bears circle in the foreground with musk ox and calf in the distance, Joel Berger © Wildlife Conservation Society

About 3,500 years ago, the last woolly mammoths died on a distant Arctic island in the Chukchi Sea. Muskoxen—mammoths’ shaggy-coated Pleistocene contemporaries—still roam the Alaskan Arctic today. Muskoxen are known to many for their distinctive huddling behavior evolved for defense against predators like grizzly bears and wolves.   Recently this prey-predator relationship has itself become the focus of a discussion on conservation tools and approaches. Continue reading

When Predators Vanish, So Does the Ecosystem

By Carl Zimmer

Mark D. Bertness, an ecologist at Brown University, began studying the salt marshes of New England in 1981. Twenty-six years later, in 2007, he started to watch them die. In one marsh after another, lush stretches of cordgrass disappeared, replaced by bare ground. The die-offs were wiping out salt marshes in just a few years.

“It’s unbelievable how quickly it’s moved in,” Dr. Bertness said.

Scientists have been witnessing a similar transformation in a number of plant species along coastlines in the United States and in other countries. And in many cases, it’s been hard to pinpoint the cause of the die-off, with fungal outbreaks, pollution, choking sediments stirred up by boats, and rising sea levels proposed as killers.

There is much at stake in the hunt for the culprit, because salt marshes are hugely important. They shield coasts from flooding, pull pollutants from water and are nurseries for many fish species.

Certain species of herbivore crab, such as this purple marsh crab, are proliferating in salt marshes where humans are trapping and fishing their main predators. CreditTyler Coverdale

In the journal Ecology Letters, Dr. Bertness and his colleagues have nowpublished an experiment that may help solve the mystery. The evidence, they say, points to recreational fishing and crabbing. A fisherman idly dangling a line off a dock may not appear to be an agent of ecological collapse. But fishing removes the top predators from salt marshes, and the effects may be devastating.

Once New England salt marshes started dying off, Dr. Bertness and his colleagues embarked on a broad survey. Quickly they noticed a difference between healthy marshes and sick ones. The dying marshes tended to be near docks, marinas or buoys where boats could anchor, or where there were other signs of fishing.

“It wasn’t a brilliant thing we thought of sitting around the lab,” Dr. Bertness said. “By the time we got to 10 marshes, we realized there was this huge disparity.”

Dr. Bertness and his colleagues wondered how fishing and crabbing were affecting the food webs of the salt marshes. If people pull out striped bass and blue crabs and other predators from a salt marsh, the animals’ prey species — including those that feed on plants, like marsh crabs — are left to thrive. A growing population of marsh crabs might wipe out the cordgrass in a marsh. Without the roots of the cordgrass to anchor the soil, the marsh would erode, making it harder for new plants to grow.

To test this idea, Dr. Bertness and his colleagues surveyed salt marshes in Narragansett Bay in Rhode Island, comparing marshes that were healthy with ones that were almost entirely dead. The scientists found that in dying marshes, the plants had more signs of being fed on by crabs. And when they looked for other proposed causes of marsh die-off, such as pollution, they didn’t find a correlation. They published their results in March in the journal PLOS One.

Next, the scientists took a step beyond simply observing the die-offs: They tried to cause them. If the predator hypothesis was right, then creating a predator-free salt marsh habitat should lead to the disappearance of cordgrass.

In May 2013, the scientists installed cages in a healthy salt marsh on Cape Cod. Each cage was three feet on a side, with mesh walls and an open bottom. Marsh crabs could feed on the cordgrass inside the cages by burrowing up through the mud, and the wire mesh walls protected them from predators like fish and blue crabs.

The experiment quickly yielded results. In a matter of weeks, the cages were crowded with marsh crabs, and much of the cordgrass inside the cages was dying off. “We were planning on it being a two- or three-year experiment,” Dr. Bertness said. “But by the beginning of July, I thought, ‘My God, this is really going fast.’”

William J. Ripple, an ecologist at Oregon State University who was not involved in the research, said, “This is an important new scientific discovery for salt-marsh systems, and more generally for ecology.” Scientists like Dr. Ripple have argued that predators are important to the ecological health of other ecosystems. But it’s been difficult to test the hypothesis directly the way Dr. Bertness has.

Merryl Alber of the University of Georgia agreed that the experiment showed that removing predators could decrease salt marsh grass. But she was reluctant to draw big lessons from the study. “It is still a leap to connect dieback to recreational overfishing,” she said.

Wade Elmer, a plant pathologist at the Connecticut Agricultural Experiment Station in New Haven, thinks that the full story of the salt marshes’ decline is more complex than just fishing. Dr. Elmer has identified a new species of fungus that attacks cordgrass in New England salt marshes. He has suggested that the fungus may weaken the plants in a way that prevents them from making chemical defenses to ward off the marsh crabs.

“I think we all have our pet theories that explain what we see in our backyard,” said Dr. Elmer, “but these theories often fail as soon as we look elsewhere.”

Dr. Bertness doesn’t rule out the possibility that other factors are at play in the die-off of marshes. But he argues that fishing is having an enormous impact.

“The implications of these findings for the conservation of salt marshes are huge,” he said. “We need to maintain healthy predator populations.”


Predator Conservation relies on understanding human psychology


Young Leopard. Bwabwata National Park, Zambezi Strip (Namibia). Credits: Ruben Portas

The world’s predators – mammals such as gray wolves, jaguars, tigers, African lions, European lynx, wolverines, and black and brown bears, along with sharks – are declining at an alarming rate. While those species are suffering for a variety of reasons, one of the main sources of mortality is human in origin. It’s a bit counterintuitive, since predators are some of the more charismatic of species. And charismatic critters are the easiest ones about which to convince people to care.

It would seem as if the best way to ensure the success of conservation programs aimed at preserving these most iconic of species would be to turn humans from enemies into allies. In other words, humans have to become more tolerant of predators. The problem, according to researchers Adrian Treves and Jeremy Bruskotter, is that we don’t know very much about what makes people tolerant of some predators and intolerant of others. In an article in this week’s issue of Science Magazine, they argue that wildlife conservation efforts ought to account for human psychology.

One of the primary assumptions driving research in conservation psychology is that intolerance toward predators, whether in the form of sanctioned eradication programs or culls (like gray wolves in the US orbears in parts of Europe or sharks in Australia) or in the form of illegal poaching, is driven mainly by the real or imagined need to retaliate against losses of livelihood, usually due to livestock predation. “Under this assumption,” Treves and Bruskotter write, “governments and private organizations aiming to protect predators have implemented economic incentives to reduce the perceived costs of predator conservation and raise tolerance for predators.”

One such program is implemented in Sweden. The government pays indigenous reindeer herders called Sami to tolerate the occasional loss of livestock to predators, and it seems to be effective for wolverines, brown bears, and lynxes. Each time a predator successfully reproduces, the Sami herders are paid.

But that strategy is only effective insofar as the source of predator intolerance is economic. That might work for some predators, but not for others. Fifty-one percent of Sweden’s wolves died from poaching between 1998 and 2009. The Swedish program has so far failed to protect gray wolves because the Sami perceive the costs of tolerance as weightier than the benefits. At present, wolves are effectively extirpated from parts of the country where reindeer graze.

An adjustment of social norms may succeed, however, where economic incentives fail. In Kenya, Maasai herders are not just compensated when lions kill their livestock; some community members are trained to warn villagers when lions approach, and monitor their movements. It reflects a different strategy, one of cautious coexistence driven by altered social norms rather than rigid defensiveness driven by externally imposed economic remuneration.

A similar effort is implemented in Brazil, for ranchers whose livestock graze near jaguar territories. In one study, researchers interviewed 268 cattle ranchers about their tolerance for jaguars, and found that perceived social norms were far more influential than economic disincentives when it came to determining any individual rancher’s likelihood to kill a jaguar. In other words, if ranchers thought that their neighboring ranchers killed jaguars, or if they thought that their neighbors would expect them to kill jaguars, they were more likely to do it. It’s the very same peer pressure that plays out in high schools across America, superimposed onto Brazilian rainforests. “The social facilitation that results in areas where poaching is common and accepted can create predator-free zones as neighbors and associates coordinate their actions explicitly or tacitly,” write Treves and Bruskotter.

Things aren’t so different in the industrialized West, where sport hunters are often thought of as valuable partners in conservation. The reasoning goes that since hunters at one time helped to conserve game species (like deer and ducks), then hunters would also help conserve predators who are designated as legal game. One program in Wisconsin was designed explicitly to increase tolerance for wolves by allowing 43 of the endangered canids to be killed each year. And yet while the program was in place, researchers found a decrease in tolerance and in increase in the desire to kill wolves. Legalizing the hunting of predators, even in a restricted way, didn’t have the intended outcome.

Wisconsin’s wolf hunting program wasn’t a controlled experiment, so the interpretation of the results is necessarily limited. However, some researchers did organize a controlled experiment to see how various approaches might improve tolerance for American black bears. The researchers discovered that providing people with information about the benefits derived from bears along with information about how to reduce the risks of negative bear encounters increased peoples’ tolerance for the animals. On the other hand, information about how to reduce risks alone, without the additional information about benefits, actually reduced their tolerance. Treves and Bruskotter suspect that’s because the risks were made more salient without the buffering effect of the bears’ benefits on local ecosystems. Similar results were seen for studies investigating the tolerance of tigers in Nepal.

Taken together, Treves and Bruskotter argue that while monetary incentives can be successful tools in the conservationist’s toolbox, poaching is influenced more strongly by social and cultural factors. “We therefore recommend caution in legalizing the killing of predators,” they say. They further argue that the best way to move forward in understanding when economic and social incentives are more or less effective is through explicit experimental manipulation, rather than through the haphazard patchwork of trial and error that has in many cases characterized predator conservation efforts. – Jason G. Goldman | 2 May 2014

Source: Treves A. & Bruskotter J. (2014). Tolerance for Predatory Wildlife, Science, 344 476-477. DOI:


Sometime last weekend a three-meter female tiger shark snared itself on a hooked line that was attached to a floating drum just off the southwestern coast of Western Australia. A commercial fisherman later motored by and, with the blessing of the government, shot it in the head. Four times.

The controversial cull began this weekend as a response to the deaths of seven people over the past three years at the hands – er, teeth – of sharks in Western Australia. At a press conference the state’s premier, Colin Barnett, said, “I get no pleasure from seeing sharks killed, but I have an overriding responsibility to protect the people of Western Australia, and that’s what I’m doing.” Protecting swimmers and other beachgoers is indeed important, but are culls even effective in the first place? And are there other methods that are better able to both protect swimmers and the sharks that many would rather avoid?

While the scientific data on the effectiveness of shark culls is scant, what data is available suggests that they aren’t terribly effective. In a 1994 paper in the journal Pacific Science, University of Hawaii researchers Bradley M. Wetherbee, Christopher G. Lowe, and Gerald L. Crow took stock of nearly two decades of shark control programs in Hawaii.

The programs were implemented with two main objectives. The obvious aim was to reduce the number of sharks in the water. In addition, data was collected from the sharks that were captured in order to add to the body of knowledge on shark biology. If the sharks were going to be killed, at least scientists could benefit from the data. At least, that was the idea.

But Wetherbee and colleagues reported that only one scientific paper derived from the shark cull data was ever published. As a result, the reports made by those who carried out the culls went unchallenged by the formal peer review process. And while the reports declared the culls successful insofar as fewer sharks were caught as time went on, a correlation does not prove causation. The researchers point out that while “the removal of nearly 4700 sharks from Hawaiian waters over an 18-yr period undoubtedly resulted in a substantial decrease in the population, and declines in shark abundance are evident in reduced catch rates in long-running programs,” other factors that could have contributed to that decline were never considered, such as predictable seasonal shifts in local shark populations, or weather patterns, which not only drive changes in shark behavior but also have a tendency to foul fishing efforts.

More damning evidence comes from the finding that there was no statistical difference between the average number of attacks per year for the eighteen years prior to the first control program and the eighteen years in which control programs were intermittently implemented. “Consequently,” Wetherbee writes with an excessive amount of understatement, “conclusions made about the effectiveness of the programs in reducing shark populations might well have been stated with less confidence.”

If culls don’t seem to work, are there any other methods for making swimmers safer? Gill nets have been shown to be effective at reducing shark encounters, but they have the downside of indiscriminately catching dolphins, dugongs, turtles, birds, rays, tuna, other non-dangerous sharks, and even whales as well. And the removal of larger sharks from the sea by drowning them in gill nets has led to the proliferation of smaller sharks in some areas, which in turn compete with fishermen for the same fish stocks. Indeed, removing apex predators can have widespread effects on the entire ecosystem, something that was made obvious with the removal and subsequent reintroduction of wolves fromYellowstone National Park.

A 2013 paper in the journal Animal Conservation describes a more welfare-oriented, ecologically conscious approach to shark attack mitigation in Recife, Brazil. The problem was that 55 shark attacks were recorded along a twenty-kilometer stretch of coastline between 1992 and 2011, 19 of which resulted in fatalities. As a result, the state government created a Committee for the Monitoring of Shark Attack Incidents, which formulated a new strategy to manage the risk of shark attacks. The guiding principle was removing sharks from high-risk areas rather than from their populations. It was actually quite simple: sharks were captured, transported, and released farther from shore. If effective, the reasoning went, such a strategy would reduce the risk of shark-human encounters while also maintaining the structure of coastal ecosystems.

Not only did the catch-and-release method avoid creating a massive ecological upset, but it was also overwhelmingly effective. Between 2004 and 2011, the shark relocation program was in operation for 73 months, and was inactive for 23 months due to funding shortfalls. Thus, researchers were able to compare the frequency of shark attacks while the program was active to months it was on hold. While the program was operational, Recife saw an impressive 97% reduction in the monthly shark attack rate.

While the shark cull program began in Western Australia last week, groups of Japanese fisherman continued their annual dolphin slaughter. It is perhaps not surprising that the kind of outrage directed towards the Japanese town of Taiji has not been aimed towards Western Australia. The cultural narrative that surrounds dolphins is one of friendliness. Dolphins are thought of as smart, playful tool-users, their faces plastered in a permanent smile. Sharks, on the other hand, are traditionally seen as little more than sets of flesh-shredding steak knives with fins. Of course neither tale is complete. Dolphins can bejerks and sharks can actually be quite clever. As shark scientist David Shiffman wrote in a recent blog post, perhaps the best strategy to avoid the needless slaughter of sharks is simply better education. Maybe swimmers can simply be taught the most effective behaviors for reducing the risk of an unfortunate encounter. Combined with a catch-and-release program, humans could then safely enjoy our brief visits to the sea. – Jason G. Goldman | 29 January 2014

Wetherbee B.M., Lowe C.G. & Crow G.L. (1994). A Review of Shark Control in Hawaii with Recommendations for Future Research, Pacific Science, 48 (2) 95-115.

Hazin F.H.V. & Afonso A.S. (2013). A strategy for shark attack mitigation off Recife, Brazil, Animal Conservation, n/a-n/a. DOI:


Hunters or Hunted? Wolves vs. Mountain Lions

Posted by Mark Elbroch of Panthera in Cat Watch

F109, a 6-yr old cougar, nursing three 3-week old kittens. Credit Mark Elbroch/Panthera

F109, a six-year-old cougar, nursing three three-week-old kittens. She wears a Vectronics satellite collar which allows researchers to follow her movements in near real time and study the secret lives of mountain lions. Photograph by Mark Elbroch/Panthera

Wolves are coursing, social predators that operate in packs to select disadvantaged prey in open areas where they can test their prey’s condition. Mountain lions are solitary, ambush predators that select prey opportunistically (i.e., of any health) in areas where slopes, trees, boulders, or other cover gives them an advantage. Thus, wolves and cougars inhabit and utilize different ecological niches, allowing them to spatially and temporally coexist; nevertheless, in the absence of wolves, cougars utilize areas traditionally assumed to be the sole dominion of coursing wolves. This suggests that where wolves are sympatric with cougars, wolves limit mountain lions.

In fact, wolves kill mountain lions. This has never been disputed. Wolves are considered the dominant competitors in most interactions between the species. Take for instance, the Hornocker Institute study of mountain lions in Northern Yellowstone led by Dr. Toni Ruth, in which researchers discovered the remains of three mountain lions killed by wolves. What is contentious is the idea that mountain lions might kill wolves.

Look carefully for the mountain lion in the background, pushed off its kill by a large wolf...caught on remote camera. Credit Teton Cougar project/Panthera

Look carefully for the mountain lion in the background, pushed off its kill by a large wolf caught on remote camera. Photograph courtesy Teton Cougar Project/Panthera

Liz Bradley, a Montana Fish, Wildlife and Parks wolf biologist, reports that she has discovered five wolves killed by mountain lions in three years—all bearing the characteristic canine punctures in their skulls betraying the identity of the perpetrator. Some dispute her claims and point out that wolves fight each other too, especially adjacent packs, and that they also attack the head; skeptics believe a canine puncture in a wolf skull could be made by another wolf just as easily as a mountain lion.

The Teton Cougar Project operates in the Southern Yellowstone Ecosystem, and is one of very few long-term studies of mountain lions. Since the start of the project, wolves have trickled into the area, established territories and reproduced. In 2001, U.S. Fish and Wildlife Service surveys estimated that there were about 10 wolves in our study area, and that number steadily increased to as high as 91 in 2010. To date, we’ve documented five lions killed by wolves, all kittens, and all less than six months old while they were still relatively slow to climb and less than fully coordinated. But it was just last October that we finally documented the contrary. For the first time, a mountain lion we were tracking killed a wolf.

She’s a particularly feral mountain lion, F109, an adult female with three three-month-old kittens. All cougars are feral, of course, but there’s something unique about F109. She has “crazy” eyes, and always wanders the most rugged, inhospitable terrain. She was near impossible to catch in the first place. She’s a survivor.

We can’t tell you exactly what happened, but we can describe what we deciphered from the clues left behind in the snow. F109 was up high traversing steep, barren slopes, where we expected there was little game. Nevertheless, her location data indicated that she’d stopped and we suspected she’d made a kill. We slogged up the mountain to investigate, the ground bare of snow adjacent the road, but as deep as our thigh in the high bowl where she lingered. The entire area preceding her position was a mosaic of wolf tracks and trails. A wolf pack made up of adults, subadults and pups had criss-crossed the area, leaving barely a patch of snow without their sign.

Perhaps the wolves had challenged F109, or perhaps just one of them wandered too close to her kittens, or perhaps a pup felt like exploring on its own—trying to decipher the absolute pandemonium of tracks was beyond us. Whatever the circumstances, F109 captured and killed a pup born this year just above the chaos of wolf activity. By this time (November), wolf pups are sizable, their skulls larger than those of coyotes. We discovered the signs of struggle, the telltale blood in the snow, and the pup’s remains beneath a lonely subalpine fir: a pile of coal black fur, bone shards from the legs, and the skull, skinned but completely intact. F109 and her kittens had consumed the pup completely.

Thus far, our research has supported exactly what everyone  expected: Wolves dominate mountain lions in most encounters. But, this recent exchange is particularly exciting. No longer can we say that wolves dominate mountain lions in all encounters. What circumstances led to F109 turning the tables, we do not know. Perhaps F109’s predecessors served as naïve intermediaries relearning to coexist with a dominant competitor, a species absent since 1926, when the last wolf was killed in Yellowstone National Park. Perhaps F109 is evidence that lions learn quickly and adapt, and that mountain lions will successfully coexist with wolves in the Yellowstone Ecosystem for generations to come.


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Cheetah do not abandon hunts because they overheat

For at least 30 years, scientists have believed that cheetahs fail to catch their prey more often than other big cats because they overheat at high speeds. But researchers in Namibia who implanted sensors in six cheetahs tell a different story. Even when one of the study animals came close to the maximum chase distance ever reported for a cheetah, his body temperature did not exceed that of his regular 24-hour average. After the hunt, cheetahs’ temperatures rose slightly, more when the hunt was successful than when it was not. The researchers attribute this temperature increase to the stress of protecting a kill from other predators.

Paper Abstract:

Hunting cheetah reportedly store metabolic heat during the chase and abandon chases because they overheat. Using biologging to remotely measure the body temperature (every minute) and locomotor activity (every 5 min) of four free-living cheetah, hunting spontaneously, we found that cheetah abandoned hunts, but not because they overheated. Body temperature averaged 38.4°C when the chase was terminated. Storage of metabolic heat did not compromise hunts. The increase in body temperature following a successful hunt was double that of an unsuccessful hunt (1.3°C ± 0.2°C versus 0.5°C ± 0.1°C), even though the level of activity during the hunts was similar. We propose that the increase in body temperature following a successful hunt is a stress hyperthermia, rather than an exercise-induced hyperthermia.


A behaviour-mediated trophic cascade involving Dugongs, Sea turtles and Tiger sharks.

‘Patterns of top-down control in a seagrass ecosystem: could a roving apex predator (Galeocerdo cuvier) induce a behaviour-mediated trophic cascade?’
By: Derek Burkholder, Michael Heithaus, James Fourqurean, Aaron Wirsing, Lawrence Dill

This manuscript presents data from a multi-year exclosure study to test a priori hypotheses regarding a behavior-mediated trophic cascade initiated by tiger sharks in a pristine seagrass ecosystem. We present evidence that seagrass communities are heavily influenced by large-bodied grazers, but only in areas where they can graze at lower risk from tiger shark predation. Although recent studies have suggested that roving predators, like tiger sharks, should be unlikely to trigger behavior-mediated cascades our work suggests that spatial heterogeneity can lead to such cascades. This study also suggests that the removal of large bodied predators could have wide-ranging consequeces for foundational species like seagrasses. Therefore, we believe that this manuscript should be of general interest to ecologists working in diverse marine, terrestrial, and freshwater ecosystems.

A behaviour-mediated trophic cascade from Journal of Animal Ecology on Vimeo.

Why top predators matter

by Jeremy Hance

Wolves chasing an elk in Yellowstone National Park. Photo courtesy of the National Park Service.

Three recent studies reveal just how important top predators are to their ecosystems.

Few species have faced such vitriolic hatred from humans as the world’s top predators. Considered by many as pests—often as dangerous—they have been gunned down, poisoned, speared, ‘finned’, and decimated across their habitats. Even where large areas of habitat are protected, the one thing that is often missing are top predators.

However, new research over the past few decades is showing just how vital these predators are to ecosystems. Biologists have long known that predators control populations of prey animals, but new studies show that they may do much more. From controlling smaller predators to protecting river banks from erosion to providing nutrient hotspots, it appears that top predators are indispensable to a working ecosystem.

Not easy being a top predator

Top predators sit at the apex of an ecosystem’s food chain. Wolves in Alaska, tigers in Siberia, lions in Kenya, white sharks in the Pacific are all examples of top predators. Some top predators have been introduced by humans, such as dingos in Australia, while others have taken over after humans have extirpated the ecosystem’s natural top predators, such as coyotes in the US after wolves and mountain lions vanished. Either way, the expanse and population of top predators has changed drastically as humans have taken over the world.

In the continental United States genetic evidence shows that there were once 200,000 wolves when Europeans arrive; today there are less than 5,000. Despite millions of dollars and years of conservation effort wolves are only present in 5 percent of their historic range in the US. Wolverines, though largely a scavenger, are terrific hunters in their own right (they are even known to harass both wolves and mountain lions). But they have it even worse in the US than wolves. While there are only an estimated 500 wolverines in the continental US, the Bush Administration denied them any coverage under the Endangered Species Act stating that wolverines still thrived in Canada, essentially arguing that this predator was unworthy of protection.

The world’s largest cats—tigers—are endangered throughout all of their range. Despite being one of the world’s most recognizable, and beloved, animals, tigers are on the edge of extinction. The species is classified as Endangered by the IUCN Red List, while two of the six surviving subspecies of tiger are considered Critically Endangered. Few animals have received the amount of conservation attention and funds as tigers, yet every year the great cat moves further from a comeback. Recent reports show tiger populations dropping in both India and Russia, both of which were considered the bright spots in tiger conservation.

Even when top predators bring in millions in tourist revenue—such as is the case of lions in Africa—they still face a barrage of trouble. Habitat loss, poisoning, and killing by gun or spear has crippled African lion populations. Recent reports state that they could vanish altogether from some of their best habitat—i.e. Kenya’s grasslands—in twenty years if nothing is done.

To think such species are somehow immune to extinction is erroneous: three tiger subspecies (the Javan, the Bali, and the Caspian), two wolf subspecies (both from Japan), one lion subspecies (the Barbary), and the thylacine—once apex carnivore in Australia—all vanished during the 20th Century. This past decade has seen the loss of the baiji: top predator and river dolphin of China’s Yangtze River.

Other top predators linger on the edge of extinction: the Amur leopard, the Indo-Chinese tiger, the Arabian leopard, the Javan leopard, and the Asiatic cheetah could all vanish during this century. In some parts of the world populations of large mammalian carnivores have dropped a staggering 95-99 percent.

It’s not just on land where top predators are vanishing. In the oceans, many shark populations have been decimated. Overfishing, by-catch, and ‘finning’ (whereby fishermen cut off a shark’s fin and then dump the animal back in the water, where it soon succumbs) are all taking a toll on some shark species. A study in 2006 found that up to 73 million sharks are killed by fining in a single year—all this to keep up orders of the Asian delicacy: shark fin soup. The first global survey of sharks and rays found that nearly one-in-three species are threatened with extinction, higher even than amphibians, which are said to be in the midst of an extinction crisis. Some shark species populations have plummeted by over 90 percent in just a few decades.

At a time when top predators are vanishing worldwide, three recent research papers show a very new side of top predators. Peeling off the dangerous, fierce veneer, these studies show that top predators are actually protectors of many aspects of the ecosystems they inhabit and show just how many detrimental ecological ripples their losses entail.

‘My enemies’ enemy is my friend’

It has long been known that top predators affect and control populations of prey species (such as wolves and elk, lion and zebra, tigers and deer), but recent studies have shown that top predators also affect carnivorous species just one rung beneath them on the food chain, known as mesopredators. Coyotes in North America, hyenas in Africa, ocelots and jaguarundis in South America, and weasels in Europe are all examples of mesopredators. 

A recent paper in Ecology Letters titled ‘Predator interactions, mesopredator release and biodiversity conservation’ reviews 94 top predator-mesopredator related studies, discovering just how much impact top predators can have on those beneath them.

The paper defines mesopredators as often “versatile generalist hunters, with a capacity to reach high population densities and have large impacts on a wide range of prey species.” However, the situation is sometimes complicated. For example, in parts of North America where mountain lion and wolves have vanished, coyotes move up from mesopredator to the apex of the food chain (top predator) though coyotes hardly practice the same hunting habits or possess the same skills as the continent’s bigger hunters.

Euan Ritchie, lead author of the paper, outlined two ways that top predators impact lesser mesopredators: these “can be referred to as fear and loathing,” he told, “first of all, top predators loathe mesopredators (think dogs and cats), perhaps through perceived competition and therefore they often actively seek them out and kill them, thereby reducing the overall abundance of mesopredators.”

According to the paper this ‘loathing’ leads a top predator to kill a smaller one “for food and to eliminate an ecological competitor.” Some top predators will kill a mesopredator and leave the body without eating it.

Secondly there are few things in the world mesopredators fear more than a run-in with a top predator: studies have shown that fear alone can cause great behavioral shifts in mesopredators.

“Fear may cause mesopredators to reduce or change their times of activity and/or habitats they use,” Ritchie explains. “This can lead to the reduced ability of mesopredators to find food, therefore lowering reproduction and survival, and hence can have large impacts on their populations.”

Through reviewing field studies, the paper found that a reduction in top predators allows mesopredators to increase disproportionately, sometimes as much as fourfold. In other words if a wolf population drops by a hundred that may allow, under certain conditions, the coyote population to explode by as much as four hundred. This ecological occurrence, termed ‘mesopredator release’ by scientists, in turn affects many other species.

As Ritchie explains: “When top predators are removed from an environment (e.g. dingoes), mesopredators (e.g. cats or foxes), which tend to be more generalist and opportunistic species with a high reproductive rate relative to larger predators, can quickly increase in abundance and drive prey species to extinction,” adding that, “this is especially true where the prey species themselves have quite low reproductive rates, such as many of Australia’s native mammals.”

For example, a population of rufous hare-wallaby vanished in Australia following the poisoning of local dingoes. Once the dingoes were gone, fox (an alien species in Australia) invaded the area and the rufous hare-wallabies, who had survived side-by-side with the dingo, were quickly hunted out of existence. Rufous hare-wallabies are listed as Vulnerable by the IUCN Red List.

In cases such as this, top predators actually aid the survival of certain prey species. By keeping a constant check on mesopredators, top predators in turn become protectors of prey species, especially smaller prey. It may not be too much of a stretch to label the world’s top predators: ‘guardians of small prey species’.

“In short,” Ritchie says, “my enemies’ enemy is my friend.” He adds that “even if large predators also occasionally eat the same prey species as mesopredators, their impact is lower relative to mesopredators, due to their larger territories and smaller overall population sizes.”

Although there is a general trend of top predators keeping a check on mesopredators—and thereby aiding a number of prey species—studying the relationship between top predators and mesopredators can prove incredibly complex. According to the paper some underlying factors that need to be considered include resource availability, habitat types, and the relationship between various predator groups.

To illustrate this, Ritchie points again to Australia: “A classic example perhaps is the relationship between dingoes, foxes and cats. Dingoes kill foxes and cats. Foxes kill cats too. The problem is that in some circumstances, by killing foxes, dingoes may be indirectly helping cats. However to date, no study has yet been able to resolve the complexity of this relationship. There’s no doubt the same situation could apply to other groups of predators, such as wolves, coyotes and cats/foxes/raccoons/skunks etc. We’re only now beginning to delve into the true complexity of these relationships.”

Despite the complexity, Ritchie and colleagues have found considerable and varied evidence of the role top predators play in regulating the ecological system.

How predators protect plants

Top predators impact prey populations, the mesopredators below them, and—indirectly—the mesopredators’ prey species, but what about plants?

At first glance it may appear ridiculous that a top predator could drastically affect an ecosystem’s plant life. However, a recent study in Biological Conservation of five National Parks in the United States (Olympic, Yosemite, Yellowstone, Zion, and Wind Cave) shows just how much plants, and thereby healthy ecosystems, rely on big predators. Not only could they be called ‘guardians of small prey species’, but in addition ‘guardians of native flora’.

During America’s short history, top predators—wolves and cougars—were largely wiped out from their habitats due to hunting, trapping, poisoning, and even government campaigns established to eradicate these ‘pests’. The study shows that this decline—and in many places complete expiration—of top predators has had drastic impacts on plants.

“The removal of top predators from landscapes allows, via reduced predation and predation risk, unimpeded foraging by large herbivores such as elk and deer,” explained Dr. Robert Beschta, lead author of the paper, to “Heavy utilization of plants by these animals, over time, can greatly alter the composition of plant communities and thus impact other animals that are dependent upon these plants as part of their life cycles.”

As an example he says that “in areas where wolves have been extirpated, greatly increased foraging pressure by elk on aspen, cottonwood, and willows can occur. If high levels of foraging continue year-after-year, this can eventually lead to the local extinction of these plants and others.”

Scientists call this process a ‘trophic cascade’, which Beschta says “is used to denote effects of predators upon their prey and, in turn, upon plants.”

Beschta and co-author William J. Ripple found that in the five parks, twenty years after top predators were displaced, tree recruitment (i.e. the number of trees surviving to designated height) declined to 10 percent of the number required to maintain historical tree communities. Within fifty years, the affect was even more acute: recruitment levels dropped to 1 percent. Eventually, the authors write, this trend would lead to many native trees’ local extinction.

The study concludes that these changes in tree survival were due to top predator loss, after carefully eliminating other possible impacts, such as climate, fires, decline in impact by Native Americans, and land use.

“None of the alternative factors explained the observed long-term declines in tree recruitment,” write the researchers.

The decline in surviving trees and the loss of particular species of plants due to predator loss can have varied impacts on the ecosystem, affecting everything from erosion to fire.

“Accelerated erosion of hill-slope soils or of stream banks can occur as the diversity and biomass of plant communities is increasingly affected,” says Beschta. In addition, “fire is an important mechanism for rejuvenating aspen stands but, in the presence of high levels of herbivory, fire accelerates the removal of large trees while sprouts and seedlings are unable to grow above the browse level of elk or deer.”

The loss of top predators—and the uptick of herbivores foraging—can also have massive impacts on aquatic environments, including degrading plant communities to a point where they “may be no longer capable of maintaining stable stream banks during periods of high flow,” says Beschta, “once riparian plant communities are degraded, increased channel widening or channel down-cutting can occur.”

Such impacts can raise summer water temperatures due to shallower streams, increase sediment runoff, and destroy important fish-rearing habitat.

A previous study in Zion National Park shows just far the loss of top predators ripples outward: the study found that abundance measurements for a number of species—including water plants, wildflowers, amphibians, lizards, and butterflies—were lower in areas where mountain lions were scarce and more abundant in areas where mountain lions still roamed frequently.

In the end, the loss of top predators can actually be linked to an overall decrease in ecosystem services, since “a diversity of native plant species, as well as the composition and structure of plant communities, are necessary to provide food-web support, maintain habitat, contribute to soil development, and a variety of other ecosystem services. The key to maintaining ‘ecosystem services’ is a healthy and vibrant plant community,” says Beschta.

But without top predators excessive grazing by big herbivores “can fundamentally alter the capability of native plant communities to function in a normal manner,” say Beschta, adding that, “unimpeded herbivory is a powerful ecological ‘force’ that can have profound consequences to terrestrial and aquatic ecosystems.”

Predators enrich the ecosystem

One of the most surprising recent studies on predators shows that not only do they affect plant species, but through hunting they actually create nutrient hotspots that keep ecosystems rich and varied.

Researchers from Michigan Technological University used a 50-year-record of moose prey kills by wolves on Isle Royale National Park, an island in Lake Superior, to find that moose corpses create hotspots of forest fertility by enriching the soil with biochemicals.

Measuring these chemicals in the soils of kill-sites and control sites, the scientists found that the soils of kill-sites were 100 to 600 percent richer in inorganic nitrogen, phosphorous, and potassium than control sites. In addition, the wolf kill-sites show an average of 38 percent more bacterial and fungal fatty acids; while nitrogen levels in foliage at kill-sites were 25 to 47 percent higher than control sites.

“This study demonstrates an unforeseen link between the hunting behavior of a top predator—the wolf—and biochemical hot spots on the landscape,” said Joseph Bump, an assistant professor in Michigan Tech’s School of Forest Resources and Environmental Science and first author of the research paper. “It’s important because it illuminates another contribution large predators make to the ecosystem they live in and illustrates what can be protected or lost when predators are preserved or exterminated.”

Bump says that he and his colleagues were shocked just how clear the biochemistry of the kill was, especially considering wolves—with the help of scavengers—pick a corpse clean.

“The fact that we observed strong effects even when carcasses are so well utilized was surprising. We suspect that the stomach contents are important in create the fertilization effects because wolves and scavengers do not eat the decomposing plant material and microbial soup in the stomachs of moose,” Bump told

If it is in fact the stomach contents that serve as the primary source of the rush of nutrients added to the ecosystem, Bump says that human hunters likely provide a similar uptick in nutrients. However, Bump adds that there is a major caveat to this.

“[Hunter-left] guts piles occur in different places and at different times of the year than wolf-killed prey,” Bump explains. “Hunter left gut piles are highly concentrated temporally during the hunting season, and are generally much closer to roads.”  In other words, wolves play an important role in the distribution of nutrient hotspots. According to the paper: “in contrast [to human hunters], wild predators hunt continuously and across a broader range.”

“Wolf-killed moose were found in some areas of the study landscape at 12 times the rate of occurrence for moose that died from other causes,” Bump says. “This means that wolves, in part, are shaping where a moose hits the ground. In some areas in which wolves apparently have greater kill-success more moose carcasses are deposited and the soil changes we observed are highly clustered.”

By clustering their kills, wolves create areas of greater soil fertility, a clustering that isn’t reproduced by human hunting, car collisions, starvation, or other means of moose mortality.

According to the paper it is unlikely that these results are unique to only wolves and moose: “The results we observed in a forest ecosystem are likely to occur elsewhere where large carnivore-ungulate relationships are intact. For example, we have observed similar above- and belowground biogeochemical effects at elk carcass sites in Yellowstone National Park, USA […] In the low resource environment of the Arctic tundra, the impact of a muskox (Ovibos moschatus) carcass on surrounding vegetation was still dramatic after 10 years, which emphasizes that carcass effects may last longer in some systems. Similar dynamics likely occur in South American, African, and Asian systems with intact large carnivore–ungulate prey relationships.”

The writers say this research is vital because it demonstrates an unknown and unexpected ecosystem service provided by top predators, which in scientific terms is described as “creating ecosystem heterogeneity at multiple scales”.

“What is important,” concludes Bump, “is that wolves are not intuitively connected to dirt and how fertile a spot of dirt may be. Identifying and describing such connections tells a more complete story of what we have when we have healthy moose and wolf populations on the landscape. If ecologists continue to tell such stories then we will understand what is lost or gained with wolf expiration or restoration respectively.”

Where do we go from here?

As researchers discover more ways in which top predators contribute to working environments, the question then becomes where do we go from here?

One relatively recent answer is to reintroduce top predators into habitat where they have been lost. To date top predators have been reintroduced into a few select areas, the most famous example being wolves in North America. But the process of reintroducing such species is new and the researchers are hesitant to recommend it without first knowing the full ecosystem picture and predicting possible effects.

“We need to take a whole of ecosystem view, and not a single-species approach,” says Ritchie, co-author of the paper on top predator impacts on mesopredators. “It is inevitable that whenever we tinker with a natural system, there will be some winners and some losers. So before we go ahead and change things, we need to ask why are we doing this, what do we hope to achieve and what are the likely results going to be? If we can’t answer these questions then we shouldn’t proceed.”

Yellowstone National Park has proven an especially intriguing example of the effects a reintroduced top predators can have on ecosystems, since the wolf, the region’s top predator, was absent for nearly 90 years.

Following the demise of wolves in Yellowstone, Beschta’s study found that Aspen populus declined rapidly due to intensified browsing by group elk herds. During this time, elk culling programs were initiated to control over-browsing in Yellowstone and other parks, but none could replicate the affect of a top predator on the ungulate populations.

Eventually in 1995 and 1996 a cautious reintroduction began in Yellowstone National Park: thirty-one wolves were returned to the wild. Despite being controversial, the measure was quickly a success.

“With reintroduction of wolves into Yellowstone, the large carnivore guild is again complete,” says Beschta. “Within a few years following reintroduction, we began to document a decrease in browsing pressure and an increase in height growth of young willows, aspen, and cottonwood in some areas. This result is extremely exciting as it appears that this is the first time in many decades that such plants have been able to grow above the browse level of elk and produce seed for subsequent generations of plants. Observations by others indicate that beaver counts are increasing and small predators and scavengers may be doing better. In contrast, elk and coyote numbers have been decreasing.”

One example of wolf impact on mesopredators—coyotes—comes from a study that shows Yellowstone has seen a fourfold recovery of juvenile pronghorn antelope.

“Overall, the reintroduction of wolves appears to have initiated a ‘reshuffling’ of Yellowstone’s ecosystem, a reshuffling that is continuing,” adds Beschta. “Over time, we hope Yellowstone will provide an improved understanding of the extent to which top predators such as wolves may have influenced other ecosystems across public lands in the American West.”

The wolves of Yellowstone are a good example of how top predator reintroductions can prove an unreserved ecological success.

Despite some remaining questions, Ritchie sees top predator reintroduction as one means to reestablish healthy, working ecosystems.

“In many situations our environments have been so badly degraded through human impacts, there is often the case to be made that we have nothing to lose and everything to gain from bold experiments,” Ritchie told “As an example, in Australia the Tasmanian devil (a native predator) is in decline in its native range of Tasmania as a result of devil facial tumor disease. This animal also used to be on the mainland of Australia until quite recently. From ecological theory and anecdotal evidence we know that this species may be able to control foxes and cats, and therefore help some of our other most threatened species. So why not introduce devils back to the mainland? They might be able to reverse some of the damage currently being done by foxes and cats, with the added benefit of establishing an insurance population of the devil on the mainland, free from disease.”

There are of course political pressures on both sides—pro-predator and anti—that complicate the issues. Many people—much like mesopredators—still fear and loathe top predators. One only has to look at the recent debate over allowing wolf hunts in the US to see how emotional the issue can become.

While the reintroduction of wolves in Yellowstone was an ecological success, politically it has proved far less smooth. After years of pressure from anti-wolf groups, this year the Obama Administration allowed Wyoming and Montana to begin hunting wolves again. Well-known Yellowstone packs were quickly devastated. No one knows yet how this latest experiment in human-managed reintroductions will impact the remaining wolves and, in turn, the greater ecosystem. Yet, for his part, Ritchie, suggests that by culling top predators, especially pack-leaders, one may worsen rather than alleviate predator-human problems.

“Many large predators (e.g. wolves) have complex social structures and behaviors, and by killing individuals, especially the older, dominant ones, we can have large impacts on how a group of animals behave,” explains Ritchie. “In the case of dingoes, there is some evidence that by killing dingoes, we are breaking down their social structure […] In some cases where dingoes are being killed, dingoes actually appear to be killing more livestock than when they were left alone. This is probably happening because few old dingoes are left, which in normal circumstances train young dogs how to hunt species such as kangaroos. So in effect what you’re left with is a bunch of rowdy, uninformed teenagers who go for the easiest target, which are often things like calves.”

Currently, Australia is mulling reintroducing dingoes to some areas in order to help over-preying on endangered native mammals. Recent research has also suggested that reintroducing wolves into the Scottish highlands (absent since the mid-1700s) could help native foliage return, which is currently over-browsed by deer. Many political difficulties stand in the way of such reintroduction schemes; in the end it’s not the science, but the politics that dictates where we go from here.

As Beschta says, “the underlying conclusion of our research is that loss of large predators has been incredibly important. Where we go next is up to society based on this ‘new’ information.”

Citations: Euan G. Ritchie and Christopher N. Johnson. Predator interactions, mesopredator release and biodiversity conservation. Ecology Letters. Volume 12, Issue 9.

Beschta, R.L. and W.J. Ripple. Large predators and trophic cascades in terrestrial ecosystems on the western United States. Bological Conservation.

Bump, J.K., Peterson, R.O., & Vucetich, J.A. 2009. Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses. Ecology. Vol 90, Issue 11.

This story was posted on on February 02, 2010, with photos and captions that are not included here. You can post a comments at:

Essential predators

Here at, My contributors and I have highlighted the important regulating role of predators in myriad systems. We have written extensively on the mesopredator release concept applied to dingos,sharks and coyotes, but we haven’t really expanded on the broader role of predators in more complex systems.

This week comes an elegant experimental study (and how I love good experimental evidence of complex ecological processes and how they affect population persistenceand ecosystem stabilityresilience andproductivity) demonstrating, once again, just how important predators are for healthy ecosystems. Long story short – if your predators are not doing well, chances are the rest of the ecosystem is performing poorly.

Today’s latest evidence comes from on an inshore marine system in Ireland involving crabs (Carcinus maenas), whelks (Nucella lapillus), gastropd grazers (Patella vulgata,Littorina littorea and Gibbula umbilicalis), mussels (Mytilus edulis) and macroalgae. Published in Journal of Animal Ecology, O’Connor and colleagues’ paper (Distinguishing between direct and indirect effects of predators in complex ecosystems) explains how their controlled experimental removals of different combinations of predators (crabs & whelks) and their herbivore prey (mussels & gastropods) affected primary producer (macroalgae) diversity and cover (see Figure below and caption from O’Connor et al.).

(a) Simplified trophic interaction network of a moderately exposed rocky shore, with the components whose presence was manipulated and highlighted in red. While mussels might not interact trophically with benthic macroalgae consistently, they can comprise important consumers of algal propagules and also have strong non-trophic interactions with macroalgae arising primarily from competition for space on the shore, which might also interact with the presence of grazers. Such strong non-trophic interactions are largely absent from food web-based theoretical frameworks yet play a key role in determining the structure of algal assemblages. While crabs can feed on whelks, no predation by crabs on whelks was observed. (b) Experimental design comprising nine treatments, involving the removal of 2 species of predator and 2 groups of their prey, to measure the independent and interactive effects of predators on primary producers and test for direct and indirect effects across trophic levels.

While there were many complex interactions and outcomes of the removals, the gist of the experiment was that the loss of either predator ended up reducing the diversity and total cover of the macroalgae, mainly via the indirect effects of altered grazing abundance. They also found that shifting the dominance of one prey species to another completely changed the dominance of different macroalgae species. Thus, the top-down effects of predators on primary producers are utterly mediated by the relative changes in prey distribution and abundance. Great stuff.

The paper is worth a read, but has a lot of provisos, methods caveats and the (typical) pleas for more experimental work over longer periods. I’m just sticking with the main message here, but it’s another case of the complexity of ecology and the necessity of trying to examine simple effects from several different angles and under several different circumstances. Yes – we do need a lot more of such studies.

Chalk this paper up as another great example of good empirical evidence for the essential role of predators. Without predators, our feeble attempts to conserve ecosystems are doomed to fail.

CJA Bradshaw.